1. Field of the Invention
The present invention relates to a power supply device suitable to supply a power supply voltage to a traveling-wave tube and the like and a high-frequency circuit system including the power supply device.
2. Description of the Related Art
A traveling-wave tube, a klystron and the like are electronic tubes used to amplify and oscillate a high-frequency signal by interaction between an electron beam emitted from an electron gun and a high-frequency circuit. As shown in FIG. 1 for instance, the traveling-wave tube has a configuration including cathode electrode 1 for emitting the electron beam, helix 2 which is a high-frequency circuit for causing interaction between the electron beam emitted from cathode electrode 1 and the high-frequency signal (microwave), first collector electrode 3 and second collector electrode 4 for trapping the electron beam emitted from helix 2, and anode electrode 5 for drawing an electron from cathode electrode 1 and guiding the electron beam emitted from cathode electrode 1 into helix 2. Cathode electrode 1 includes heater 6 which provides heat energy for emitting a thermion from cathode electrode 1.
The electron beam emitted from cathode electrode 1 is accelerated by a potential difference between cathode electrode 1 and helix 2 and introduced into helix 2, and proceeds inside helix 2 while interacting with the high-frequency signal inputted to helix 2. The electron beam outputted from helix 2 is trapped by first collector electrode 3 and second collector electrode 4. In this case, the high-frequency signal amplified by the interaction with the electron beam is outputted from helix 2.
As shown in FIG. 1, cathode electrode 1 is supplied with helix voltage (HELIX) which is a negative direct-current voltage on the basis of the electric potential of helix 2. First collector electrode 3 is supplied with first collector voltage (COL1) which is a positive direct-current voltage on the basis of the electric potential (H/K) of cathode electrode 1. Second collector electrode 4 is supplied with second collector voltage (COL2) which is a positive direct-current voltage on the basis of the electric potential (H/K) of cathode electrode 1. Anode electrode 5 is supplied with anode voltage (A) which is a positive direct-current voltage on the basis of the electric potential (H/K) of cathode electrode 1. And heater 6 is supplied with a heater voltage (H) which is negative direct-current voltage on the basis of the electric potential (H/K) of cathode electrode 1. Helix 2 is normally connected to the case of the traveling-wave tube that is grounded.
Helix voltage (HELIX), first collector voltage (COL1), second collector voltage (COL2), anode voltage (A) and heater voltage (H) are generated by using an inverter for converting the direct-current voltage to an alternating voltage, a transformer, a rectifier circuit, a rectification capacitor and the like. Bleeder resistances R1 and R2 are connected between helix 2 and first collector electrode 3 and between first collector electrode 3 and second collector electrode 4 for the sake of suppressing a rise in first collector voltage (COL1) and second collector voltage (COL2) generated by a change in the balance of currents passing through first collector electrode 3 and second collector electrode 4 at a low load current.
FIG. 1 shows a configuration example of a traveling-wave tube including two collector electrodes. However, there are also configurations of the traveling-wave tube including only one collector electrode and including three or more collector electrodes. In the case of the configuration including three or more collector electrodes, the bleeder resistances are connected to each of the rectifier circuits for generating collector voltage (COL) supplied to each of the collector electrodes respectively. Resistances of a relatively large value (several MΩ or so) are used as bleeder resistances R1 and R2 for the sake of reducing the current when the traveling-wave tube is operated.
A power supply device for supplying a power supply voltage to each electrode of such a traveling-wave tube is required to supply the traveling-wave tube with heater voltage (H) first to preheat cathode electrode 1 (for 3 to 5 minutes or so) and supply helix voltage (HELIX), anode voltage (A) and collector voltage (COL) after completion of preheating. Therefore, a conventional power supply device adopts a configuration which includes a first high-voltage transformer for generating helix voltage (HELIX), anode voltage (A) and collector voltage (COL) and a second high-voltage transformer for generating only heater voltage (H) so as to control the order of application of power supplied to primary windings of the two high-voltage transformers.
However, a heater power supply for supplying heater voltage (H) needs to secure isolation performance for the sake of using it at a high-voltage potential despite a small current capacity required so that it needs to use an expensive large-size high-voltage transformer. For that reason, there is an increase in circuit size and cost of the power supply device.
Thus, Japanese Patent Laid-Open No. 09-017344 (hereinafter referred to as Patent Document 1) describes a high-voltage power supply circuit wherein the power supply dedicated to the heater is no longer necessary and a high-voltage transformer for that purpose is eliminated. The high-voltage power supply circuit described in Patent Document 1 includes a helix power supply, an anode power supply, a heater/collector power supply connected to a heater power supply and a collector power supply, a relay for interrupting the collector voltage outputted from the heater/collector power supply, a discharge circuit for discharging the collector voltage at an output terminal, and a power control circuit for controlling the order of application of the power supply voltage.
As for the high-voltage power supply circuit described in Patent Document 1, the heater/collector power supply is turned on to supply only the heater voltage in which the collector voltage is interrupted by using the relay (high-voltage vacuum relay). After completion of preheating of the cathode electrode, the heater/collector power supply is once turned off, and an electric charge at the output terminal of the collector voltage is discharged by using the discharge circuit. After completion of the discharge, the helix power supply, anode power supply and heater/collector power supply are all turned on so as to eliminate the need for a high-voltage transformer being dedicated to the heater.
As described above, the conventional power supply device for the traveling-wave tube includes the power supply dedicated to the heater. Therefore, it is necessary to include multiple, expensive large-size high-voltage transformers, and so there is a problem that the power supply device becomes larger and the cost increases.
The above-mentioned bleeder resistance connected between the helix and the collector electrode has a high applied voltage so that consumed electric power is large even though the amount of current passing through it is small. Thus, a package of bleeder resistance becomes large in order to acquire sufficient withstanding electric power. For that reason, there is a problem that the implementation area of the bleeder resistance becomes large. In the case where the bleeder resistance is not used, it is necessary to use a high-voltage regulator circuit whose variable capacity is large so that the collector voltage becomes stable even if the load current significantly fluctuates in a short time. Therefore, it is not possible, even in such a configuration, to avoid an increase in the circuit size and cost of the power supply device.
A high-frequency circuit system including the traveling-wave tube and the power supply device thereof is used not only for various radio communications and terrestrial broadcasts but also for satellite communications and satellite broadcasts or mobile communications. Therefore, there is an increasing demand for miniaturization, lighter weight and cost reduction of the system.
The above-mentioned high-voltage power supply circuit described in Patent Document 1 is effective at rendering a power supply that is dedicated to the heater unnecessary and reducing the number of expensive and large-size high-voltage transformers. However, the circuit cannot reduce other large-size parts such as the high-voltage vacuum relay and bleeder resistances. Thus, it is not sufficient for achieving further miniaturization and cost reduction.